If you buy a ring at a flea market, usually the best-case scenario is that it doesn’t turn your finger green. Well . . . this woman’s story just redefined that best-case scenario.

A woman in London, England paid $15 for a costume jewelry ring at a flea market about 30 years ago. She liked how it looked, so she wore it all the time.

But earlier this year, a jeweler saw it and told her she should have it appraised because it looked real. So she took it to Sotheby’s, they checked it out . . . and, yeah, it turned out to be an actual diamond ring.

The “costume jewel” was actually a 26.67-carat diamond that’s worth approximately $450,000.